1. Field of the Art
The invention is a method and apparatus for interactively controlling color correction in photographic reproduction. In particular, the invention relates to determining the optimum settings for gamma correction curves which are then used by a photographic reproducing device.
2. Related Art
One conventional method for color correction when preparing photographs for reproduction employs gamma correction curves. The use of such gamma correction curves was disclosed by Korman in U.S. Pat. No. 3,612,753 issued in 1971. As discussed in column 8 of Korman, an original picture is scanned and for each point scanned signals are developed which are proportional to red, green and blue color densities. Density is defined as the logarithm of reciprocal of the amount of light reflected from a opaque copy or transmitted through a transparency. The three color density signals are converted to their digital equivalents and stored using three parallel channels. Equivalent neutral densities (END) of cyan, magenta, yellow and black inks necessary to reproduce the color in question are then determined. The equivalent neutral densities for cyan, magenta, yellow and black are determined by experiment while the color densities of red, green and blue are calculated. Korman does not disclose controlling or adjusting the stored gamma correction curves themselves.
U.S. Pat. No. 3,893,166 to Pugsley issued in 1975 discloses color correcting image reproducing methods and apparatus. In Pugsley, a computer stores different tone characteristic curves. A control panel permits selecting one of these curves and permitting the end points of the selected curve to be shifted. An analyzing head is directed at selected points on the colored original to generate blue, green and red filter color component signals corresponding to yellow, magenta and cyan printer signals respectively. A-D converter 23 then converts the signals to digital form to facilitate operation of first software stage 24A for tone characteristic selection in computer 24. Tone corrected signals are then subjected to color correction. Basic color correction data is stored in the computer in software stage 24B but can be modified for editorial correction by controls on sub-panel 29D of control panel 29. As discussed in column 6, lines 34-56 of specification, as many as 18 individual controls are needed on sub-panel 29D to modify or perform editorial correction of the basic color correction stored in the computer software stage 24B. Thus, an operator can be overwhelmed with the numerous individual adjustments required.